1. Field of the Invention
This invention relates to the field of voltage reference circuits, and particularly to a voltage reference circuit fabricated with complementary metal oxide semiconductor (CMOS) devices.
2. Background Art
In the design of large scale integrated circuits, it is often necessary to provide a local reference voltage of a known value that remains stable with both temperature and process variations. A common prior art approach is a bandgap reference circuit. Such circuits develop a stable reference voltage that is approximately equal to, or a ratio of, the bandgap voltage of silicon (i.e., about 1.2 volts). Bandgap reference circuits are noted for their stability, but are generally implemented with bipolar devices and are relatively complicated, particularly if it is necessary to operate over a wide swing in the power supply voltage.
Five volt power supplies, which have long been the standard for bipolar transistor circuitry, have also been widely used for CMOS circuitry. However, there has been a growing trend toward the use of lower voltage supplies for CMOS devices. Typically, these provide power at approximately 3 volts. In view of this trend to lower voltage power supplies, it is desirable to design new CMOS devices so that they are capable of operating over a wide range of power supply voltages.